A rail, as is apparent from the section thereof shown in FIG. 1, consists of a foot portion R1, an ankle portion R2, a web portion R3, a head portion R4 and a head top plane R5. To butt-weld rails by field facilities, conventionally thermite welding technique or enclosed arc welding technique is applied. In the enclosed arc wel technique, weling is continuously performed: a coated arc welding rod is used; multilayer welding is conducted on the rail foot portions R1; and then the web portions R3 and the head portion R4 are surrounded with enclosed block members.
However, any automatic fusion welding technique using a filler wire has been not yet placed into practice. In the thermite welding, (1) the performance of joints is poor, and is statistically liable to be broken during use, and (2) skill is necessary for operation. On the other hand, the enclosed arc welding technique has problems in that: (1) skill is needed for operation; (2) working environment is bad due to high preheat temperature; and (3) productivity is low. Thus, it is desired to develop an automatic fusion welding to be high efficiency and high performance without need for skill.
From the purpose of use of a rail, it is required to have quality of high wear resistance at the top plane R5 against rolling contact with wheels and resistance against fatigue cracks, that is, fatigue damage resistance. On the other hand, the foot portion R1, the web portion R3 and the head portion R4 are required to have static strength and fatigue strength to withstand impacts or bending loads during passing of wheels, and furthermore it is necessary to have no welding defect, such as weld cracks, or have a defect as little as possible so as to provide no problem in practical use.
Under these situations, various kinds of automatic fusion welding which will be able to replace for the thermite welding and the enclosed arc weld in the future have been studied. Techniques disclosed in Japanese Patent Examined Publications Nos. 44-24249 and 45-14173 were proposed as a method to replace the enclosed arc welding. According to the former technique, rail bottom portions are welded by the multilayer submerged arc welding, and rail web portions and head portions are welded by the electroslag welding. On the other hand, the latter performs welding over the whole sectional areas of the rails by the gas shielded arc welding. Also, techniques taught in Japanese Patent Examined Publications No. 45-19369 and Japanese Patent Unexamined Publication No. 61-249679 conduct a method of butt-welding rails using the gas shielded arc welding.
These above-mentioned prior art still have many problems in utility although the techniques do not need application of pressure in the rail axial direction, and in these techniques it is possible to enhance efficiency as compared to the enclosed arc welding.
More specifically, according to the former, welding is conducted while slag is removed during the submerge arc welding, welding is temporarily discontinued after the welding of the bottom portions is completed, and then welding is restarted to carry out the electroslag welding of the web and the head portions. Accordingly, it is likely that weld defects, such as lack of fusion and solidification cracks, take place each time when welding is started and stopped. Further, welding is deteriorated in efficiency. Furthermore, in the welding of the rail bottom portions and the web and the head portions, it is necessary to properly use welding materials (such as flux) and to switch characteristics of the welding power source. Thus, this method involves deterioration in efficiency due to complicated operation, cost up of the welding machine and complicated control of welding materials.
On the other hand, the latter method overcomes such defects, but in view of the technique being applied to field construction, it is inferior in that sufficient attention must be paid to wind resistance since a shield gas is used in the whole sectional areas of the rails. Particularly, it is very hard to perfectly shield the rail web portions to the rail head portions from wind in the field to thereby keep the gas shield effect properly, and even if possible, a complicated mechanism is needed and is not practical. Furthermore, the gas shielded arc welding is narrower in proper welding condition range to bevel size than the electroslag welding. Particularly, when layering of welding proceeds, in regions from the rial web portions to head portions there is a high possibility that weld defects, such as poor fusion, take place due to variation of bevel size, and hence it is liable to deteriorate reliability of the joint.